Joe Schwarcz: PCBs are not 'toxic time bombs'; The potential for risk from the illegally stored waste in Pointe-Claire is being blown out of proportion

We hadn’t heard much about polychlorinated biphenyls since the fire at St-Basil-le-Grand in 1988, but we sure are hearing a lot now.

There are two angles to news about the illegally stored PCB-filled transformers and contaminated waste in Pointe-Claire. There is the legal and political story, and there is the scientific one.

Without question, the PCBcontaining materials were improperly and illegally stored and will have to be removed and properly processed. That is the law.

But when it comes to the science, the risk posed by the chemicals and the “toxicity” of PCBs have, in my view, been exaggerated, generating an unwarranted degree of public anxiety. One got the impression a cache of nerve gas had been discovered; headlines screamed about “toxic time bombs” apparently ready to explode. In fact, PCBs are not the devil incarnate.

PCBs are non-corrosive, non-conducting, fire-resistant chemicals that were widely used in transformers, fluorescent-light ballasts and hydraulic machinery until the late 1960s. It was then that an incident in Japan drew attention to their potential toxicity: About 1,500 people became ill after consuming rice oil that had been contaminated with PCBs, which were used at the time as a heat-transfer medium in a process to deodorize the oil.

Because the PCB-based heat-transfer liquid was heated to 200 C, there was a conversion of some of the PCBs to polychlorinated dibenzofurans, which are far more toxic than PCBs and were the probable cause of gastric symptoms, jaundice, eye discharge and skin eruptions. Some long-term consequences were also noted: Women who had consumed the contaminated oil during pregnancy gave birth to slightly smaller babies, who also experienced developmental problems.

But numbers and measurements are critical to science. The Japanese victims consumed somewhere between half a gram and two grams of PCBs – several million times more than the amount anyone in North America could be exposed to even if he or she consumed fish from the most PCB-contaminated waters.

The Japanese accident unleashed a flurry of research about the toxicological impact of PCBs. Electrical-industry employees were extensively surveyed but few problems surfaced, even among those who had spent 30 years working elbow-deep in PCBs. There was an observation of slightly higher death rates from rectal and liver cancers, but this was contentious because lifestyle characteristics such as alcohol consumption and diet had not been appropriately controlled for.

Animal experiments, on the other hand, clearly showed that PCBs were toxic and even capable of triggering cancer. But again, let’s look at the numbers. If we assume that humans react in a way similar to rats, a daily dose of eight milligrams of PCBs per kilogram of body weight would be required to possibly cause a problem. This is about 500,000 times greater than what the average person is exposed to on a daily basis. Still, the data were enough to classify PCBs as “probable human carcinogens.” That classification is often misinterpreted. It just means that a substance is capable of causing cancer at some dose under some sort of exposure.

One further concern is that PCBs have possible hormone-disrupting properties, and that may indeed be the case. But there are numerous substances, both natural and synthetic, to which we are exposed that have such effects. In any case, for there to be any significant consequences, there would have to be long-term exposure in the form of contaminated food.

Basically, then, PCBs are not particularly toxic. Benzene, to which we are regularly exposed from gasoline, benzopyrene, from wood-burning stoves, and the heterocyclic aromatics in barbecued foods are more “toxic.”

Now, back to Pointe-Claire. PCBs have very low volatility, and the trace amounts that evaporate dissipate quickly in the air. As for possible ground contamination: PCBs are very insoluble and bind to sediment. Trace amounts may be detected in the water table under the site, but this is not the water that runs from taps.

If PCBs have such low toxicity, why were they banned? Two reasons. They are extremely stable compounds and do not break down in the environment, which means that further production would increase the amount dispersed around the globe and create a difficult situation should significant adverse effects come to light in the future. Second, PCBs are fat-soluble, so they are not readily eliminated through urine and build up in the food chain. Continued release into the environment would lead to increased body loads with possible health consequences. Given that alternative chemicals were available, the ban was reasonable, although there is no guarantee the replacement chemicals will be less problematic.

In any case, neither storing PCBs illegally nor withholding information by governments can be condoned, particularly because a fire at such a facility could result in dangerous furans and dioxins being released. But I believe the chance that the stored PCBs could be linked to any adverse effects borders on zero.

The effects of the stress caused by the unrealistic portrayal of a “toxic time bomb” may, however, not be zero.

joe.schwarcz@mcgill.ca Joe Schwarcz is the director of McGill University’s Office for Science & Society (mcgill.ca/oss) and author of the column The Right Chemistry, which appears Saturdays in The Gazette.

Comments

We encourage all readers to share their views on our articles and blog posts. We are committed to maintaining a lively but civil forum for discussion, so we ask you to avoid personal attacks, and please keep your comments relevant and respectful. If you encounter a comment that is abusive, click the "X" in the upper right corner of the comment box to report spam or abuse. We are using Facebook commenting. Visit our FAQ page for more information.

Video

Dress for the Weather

Classified

Buy, sell and trade smarter.

Stories, pictures and tributes to life. View and place obituaries, and more.

Share the joy. Tell the world. Read and place announcements here.

The faster, fresher and greener way to shop flyers.

Find the job you want in your city. View and place job listings, and more.